Vibration/ Low Grinding/ Rattle

[cobrabuilderI]

Gentlemen-
After my post concerning the fuel delivery problem, had something ELSE ---
Picked up my nephew from my sisters house to take him up to my folks for dinner last night. Was all happy my baby was going to be okay with the fuel problem fixed and was running nice. Ran it for 20 mins. to pick him up and then we left and ran it about 15 min. or so, got on straight away after turning corner and I hit it. Took it up to 6 on the tach on each gear to 70 mph then came back down to 55. After I did that and was still on road, when I would engage clutch, or put gears in neutral, there was a sound like grinding- not real bad grinding like when you put it in reverse with it running but like a low grinding/ scraping noise. It only made that noise at higher speeds like 55 mph and then let off. IT was almost like a vibration. At first the noise wasn't bad, but the more I drove it the worse it sounded. Got to my folks ate dinner, and came home, it was doing the same thing. As long as I was running with gears engaged it was fine, which, by the way all the gears worked fine and the clutch worked fine everything worked great except for that noise. Let off the rpm and that noise would start. It hadn't done that before at all. I thought it might be the clutch plate might still be engaged somewhat as I do have a hydraulic clutch that has some adjustment. Any thoughts?

[Big-Foot]

Have you had any work done on the rear end? Differentials will act that way when the gears are having "interface" problems. When the lube is cold, the noise is much less or almost non-existant. As the lube warms up, the noise and vibration increase with intensity. The noise and vibration will come and go as you load or unload the differential also.

I would put her up in the air and see how much rotational backlash you have with the pinion.

[cobrabuilderI]

Randy-
Thanks Bro.
Yes I have done some work - I had to change bearing on driver side as it was leaking for some time but I meant to check it and didn't before I left- the people at Currie said as long as I wasn't taking here cross country I'd be okay- that's why wasn't concerned too much. The is probably a little low- will check. As far as the backlash with the pinon what should it be- this is the yoke right that attaches to the drive-shaft?

-
Bruce

[Big-Foot]

Yes - it's the yoke that attaches to the driveshaft.

Running the diff low on gear oil doesn't hurt the gear interface as much as it hurts the pinion bearings. I hope you didn't run her too low..

I don't know what rear end you have but both 8.8" & 9" Fords typically run between .008 and .012" of backlash. In terms of how many degrees of rotation that might be on the pinion / Good question - and I can't answer it.
What I can tell you is that - properly setup - the pinion will rotate only enough to tell you that there is "some" clearance between the pinion and ring gear. If you can rattle it back and forth a good distance - you have a problem.
Another thing to check is the backlash in different positions. Looking at one of the wheels, rotate it so the valve stem is at 12 O'Clock - check backlash. Now rotate to 3 O'Clock and check again. Go through the 6 and 9 O'clock positions and check backlash as well. It should be an identical amount of backlash all the way around. If not - it's time to pull her apart before she pulls herself apart..

[cobrabuilderI]

Randy-
Thanks for your help-
If you're ever in Tampa call me up= I'll be happy to buy you a beer if you're ever in FLORIDA>
That worked out great! I checked it this afternoon and ran the baby for 50 miles or so and all was good. My upper link bars were also not set right as the shock was not level ( at least eyed not right ) and adjusted so that they were level and all seem good. Thanks for your help=

Bruce

[CowtownCobra]

Bruce, I had a similar problem. Turned out my drive shaft was 1 1/2 inches too short. Only showed up at highway speeds when backing off the throttle and coasting. Go over to dennys driveshafts www.dennysdriveshaft.com and check out the proper procedures for measuring the driveshaft. If thats what it is, it will eventually tear out the back of your tranny.

[Big-Foot]

Bruce - Pinion angle was going to be my next suggestion. Typically the pinion angle will not change between hot/cold but shocks will and that was probably what you were up against. Glad you got that worked out!